The other surprise was where the fossils were found: in southern Germany, far from modern hummingbird territory. To some scientists, the discovery shows that hummingbirds once existed outside the Americas, then went extinct. Or maybe the fossils weren't true hummingbirds. Skeptics, including Schuchmann, argue that other groups of birds evolved hummingbird-like characteristics many times through the eons. True hummingbirds, says Schuchmann, evolved in Brazil's eastern forests, where they competed with insects for flower nectar.

"Brazil was the laboratory for the prototype," he says. "And it worked." Hummingbirds became nature's micro-engineering masterpieces, perfecting their hovering ability tens of millions of years ago to compete for a share of the New World's flowers.

"They're a bridge between the insect and bird worlds," says Doug Altshuler, who studies hummingbird flight at the University of California, Riverside. Altshuler has examined hummingbirds' flapping motion and observes that the electrical impulses that drive their wing muscles look more like those of insects than those of birds, which may explain why hummingbirds produce so much power per stroke—more, per unit mass, than any other vertebrate. Altshuler has also analyzed their neural pathways, which function with the lightning speed of the most agile birds, such as their closest cousins the swifts. "They're amazing little Frankensteins," Altshuler says.

They are certainly fearsome—gram for gram, perhaps the most confrontational players in nature. "I think the hummingbird vocabulary is a hundred percent swear words," says Sheri Williamson, a naturalist at the Southeastern Arizona Bird Observatory. Their aggression stems from fierce territorial instincts shaped by their need to sip nectar as often as every few minutes. Hummingbirds compete by challenging and bullying each other. Face-to-face in midair, they post up and pirouette, dive to the grass, and paddle backward in dances of dominance that end as suddenly as they begin.

These battles are best observed in mountains, especially tall ones near the Equator that offer rich ecosystems at a variety of elevations. Williamson suggests that the north-south orientation of mountain chains in the Americas also creates favorable migration highways with a constant source of flowers. Compare that, she says, with natural barriers in Africa that stretch east to west, such as the Sahara and the Mediterranean Sea.

A few hummingbird species, however, have adapted to crossing vast, flat expanses where food is scarce. Before their daunting spring migration to the United States and Canada, ruby-throated hummingbirds gather in Mexico and gorge on insects and nectar, storing fat and doubling their weight in a week. Then they launch across the Gulf of Mexico, flying nonstop for 20 hours and 500 miles (800 kilometers) to the far shore.

Ninety-five percent of the world's hummingbird species occur south of the U.S.-Mexico border. In the first moments out of the airport in Quito, Ecuador, you might be greeted by a sparkling violet-ear with iridescent splashes of war-paint purple on its cheeks. East of the city in the highest reaches of the Amazon watershed, the swordbilled hummingbird floats amid dense greenery, hoisting the longest bill of any bird for its body size—more than half the animal's total length. On the slopes of Cotopaxi, a volcano south of Quito, the Ecuadorian hillstar has been spotted above 15,000 feet (460 meters). There it spends the night in caves and enters torpor, curbing its metabolic rate enough to avoid starving before dawn. Later, warmed in sunlight, the hillstar powers up and resumes feeding.